In construction engineering, some of the most important properties of interest are volumetric and mechanistic properties of a bulk soil mass. In particular, there are procedures in construction engineering practice that relate total volume Vt, mass of water MW, and mass of dry solids MS to the performance of a structure built on a soils foundation. Thus, the measurements of these properties are important for construction engineering.
Material density and moisture content are other important material properties used for design, quality control, and quality assurance purposes in the construction industry. Some exemplary techniques for measuring the density and moisture content of soils include nuclear, sand cone, and drive cone, as described by the American Society of Testing and Materials (ASTM) standards D-2922, D-3017, and D-1556, and the American Association of State Highway and Transportation Officials (AASHTO) standards T-238, T-239, T-191, and T-204. The nuclear measurement technique is non-destructive and calculates both the density and the moisture content in a matter of minutes. The sand cone and drive cone measurement techniques require the moisture content test of ASTM standard D-2216, which involves a time consuming evaporation process. The moisture content test involves heating a sample to 110° C. for at least 24 hours.
For road construction, there is an optimum water or moisture content that allows for obtaining a maximum density. An exemplary density test is described in ASTM standard D-698, wherein a field sample is prepared with different water contents, and compacted with like energy efforts. Hence, each sample has different water content, but the same compaction effort. The densities are then measured gravimetrically in the laboratory. The moisture content with the highest density is deemed the optimum condition and selected as the field target. Summarily, the objective of material compaction is the improvement of material properties for engineering purposes. Some exemplary improvements include reduced settling, improved strength and stability, improved bearing capacity of sub grades, and controlling of undesirable volume changes such as swelling and shrinkage.
In the road paving and construction industry, portable nuclear density gauges are used for measuring the density of asphalt pavement and soils. Often, an asphalt paving material is applied on a new foundation of compacted soil and aggregate materials. The density and moisture content of the soil and aggregate materials should meet certain specifications. Therefore, nuclear gauges have been designed to measure the density of the asphalt pavement and soils.
Nuclear density gauges typically include a source of gamma radiation which directs gamma radiation into the sample material. A radiation detector may be located adjacent to the surface of the sample material for detecting radiation scattered back to the surface. From this detector reading, the density of the sample material can be determined.
These nuclear gauges are generally designed to operate either in a backscatter mode or in both a backscatter mode and a transmission mode. In gauges capable of transmission mode, the radiation source is vertically moveable from a backscatter position, where it resides within the gauge housing, to a series of transmission positions, where it is inserted into holes or bores in the sample material to selectable depths.
Nuclear gauges capable of measuring the density of sample materials have been developed by the assignee of the present subject matter. For example, nuclear gauges for measuring the density of sample materials are disclosed in U.S. Pat. Nos. 4,641,030; 4,701,868; and 6,310,936, all of which are incorporated herein by reference in their entirety. The gauges described in these patents use a Cesium-137 (Cs-137) source of gamma radiation for density measurements, and Americium Beryllium (AmBe) neutron sources for moisture measurements. Paving material may be exposed to the gamma radiation produced by the Cs-137 source. Gamma radiation is Compton scattered by the paving material and detected by Geiger-Mueller tubes positioned to form at least one geometrically differing source-to-detector relationships. The density of the paving material is calculated based upon the gamma radiation counts detected by the respective detectors.
One difficulty to the use of nuclear density gauge is the use of a radioactive source and the associated regulations imposed by the U.S. Nuclear Regulatory Commission (NRC). The requirements for meeting NRC regulations are largely dependent on the quantity of radioactive source material used in a gauge. Thus, it is desirable to provide a nuclear density gauge having a smaller quantity of radioactive source material in order to reduce the requirements of the NRC for use of the gauge.
Another difficulty with nuclear gauges is the time required for making a density measurement of material. Delays in obtaining density measurements of soils during construction may delay or otherwise disturb the construction process. Thus, it is desirable to provide a nuclear density gauge operable to provide faster density measurements.
Accordingly, in light of the above described difficulties and needs associated with nuclear density gauges, there exists a need for improved methods, systems, and computer program products for measuring the density of material.